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Contemporary electronic systems, particularly industrial or enterprise scale computer or networking systems, typically utilize a physical/mechanical design wherein the various components of the system reside on a number of individual circuit boards which are interconnected via a common backplane circuit board. This type of physical implementation has the advantages of efficient and economical component interconnection and use of physical space, especially for highly reliable/redundant systems, as well as allowing for efficient and economical cooling and maintenance. Electronic backplanes, also referred to as motherboards, serve as a communication medium for the exchange of electronic signals between the various circuit boards. These same backplanes also serve as a vehicle for providing electrical power to the circuit boards.
Power is generated, i.e. converted from a source/input into various voltages and currents required by the various system components, at one or more power supplies and is distributed to the circuit boards via the backplane. A backplane is itself a printed circuit board, often having multiple layers, with a number of sockets/connectors mounted thereon for receiving the other circuit boards which make up the system. The backplane contains the wiring, also referred to as traces, to interconnect the circuit boards, i.e. signal traces or signal busses, as well as provides and distributes power to the circuit boards, i.e. power distribution traces, busses or power rails.
In one prior art system, the system power converter/supply is itself carried on one of the circuit boards plugged into the backplane. The system power supply receives AC power from the local power grid and provides one or more DC voltages to the backplane via its interconnect. Each of the other circuit boards plugged-in to the backplane receives these DC voltages via the power distribution traces and uses the voltages as needed to power their circuitry. Most of the circuits used in typical electronics/computer applications require lower voltages to operate, typically 1.8, 2.0, 3.3 and/or 5 volts. The power supply/converter converts the AC input into the necessary lower voltages. To ensure fault tolerance, an additional redundant system power supply may be provided, often referred to as N+1 redundancy. However, a number of problems have been recognized with this approach. For example, because all of the system components derive their operating power from a single power supply or set of power supplies as well as share a common ground plane, it is difficult to isolate faults to a failing component and minimize collateral damage to functioning components. Further, the additional power supply rails in the backplane use more of the available spaces in the backplane sockets as well as more of the available trace routing area, increase resistive losses and increase system noise. These problems are exacerbated in more advanced systems wherein higher current demands necessitate a more robust power distribution architecture, i.e. thicker and/or more numerous traces. In addition, the power supply/converter consumes a valuable slot on the backplane which could be used for another circuit board. In fault-tolerant/redundant systems, the redundant power supplies consume even more available space/slots.
Use of a distributed power arrangement rather than a centralized arrangement avoids these problems. In a distributed power system, the main power supply provides only one relatively low current/high voltage level, typically 12 to 48 volts, to the backplane, also referred to as an intermediate voltage. The lower voltages are provided by power converters located directly on each circuit board. This helps reduce system noise by isolating functional blocks and allows for some measure of failure isolation. Further, each converter can be optimally sized for the functional circuitry on its own circuit board. In addition, the main power supply need not be closely regulated, since the distributed converters provide control on each board. However, in this configuration, the DC power converters consume valuable circuit board space and create electrical noise and heat on the circuit boards. Further, because each circuit board requires separate DC-input power supplies, the system level cost is significantly increased. In systems requiring redundant components for reliability, redundancy for DC-input power supply fault tolerance requires duplication of components on each circuit board, greatly increasing cost and occupation of space. In addition, power converters located on the circuit boards may interfere with hot swapping, i.e. plugging in or removing boards while the power is on.
In another prior art system, one or more free-standing, separately housed power supplies are mounted within the system enclosure and connected to the backplane via bundles of high-current capacity wires or solid metal distribution bars, known as bus bars, to supply power to all of the circuit boards in the system. These free-standing power supplies are typically self-contained power supply systems, having their own enclosures. This configuration yields several undesirable performance problems. The power supply enclosure adds to the physical weight, cost, and size of the power supply. This configuration typically includes a cooling fan that must be integrated into the airflow management design of the enclosure further adding cost and addition acoustic noise. Since current drawn from the power supply is application dependent, the current capacity of the power supply often must change with application, necessitating a change in the power supply configuration. As free-standing units, the power supplies are coupled to the backplane via bus bars or bundles of high-current wires. The size, quantity, and configuration of these wires is application dependent and therefore must be reconfigured according to the application and current capacity thereof. Because the power rating of the power supply is driven by the worst case requirement of any single direct current (DC) voltage, the power supply selected for an application is typically larger than required. These power supplies tend to be available in standard sizes that offer limited choices, for example such that a need for increased current at 5 Volts will result in more current being generated at the other voltages as well, even if not required for the application.
Further, contemporary system applications demand fault-tolerant operation. This demand drives a need for fault-tolerant, redundant power supplies having current sharing and hot swap capability. A typical embodiment employs fully redundant power supplies, significantly increasing physical space, weight, and cost. Assuming that each unit is a free-standing power supply with multiple output voltages and high-current capacity, a small number, for example 3, power supplies are commonly employed in redundant systems. This requires significantly more power capacity, for example 50%, than a non-redundant system, such that the system will continue to perform with uninterrupted operation if one of the power supplies fails.
In addition, another problem with redundant solutions in prior art system is that, because the redundant power supplies are connected together with the load, the redundant supply must remain turned off when the main supply is operating correctly, in order not to overload the load or connections therewith. When the main supply fails, the redundant supply must then turn on to keep the load operating. The delay in ramping up the redundant supply to full power must be accounted for in the operational characteristics of the load so that the load does not fail due to the interruption. This necessarily places design constraints on the design of the load circuit board. Further, the second power supply must not accidentally power on while the first power supply is active or catastrophic results may occur due to an overload.
Accordingly, there is a need for a power supply and distribution system which provides redundant/fault-tolerant operation while supporting high current demands with reduced electrical noise. Further, there is a need for a power supply and distribution system which isolates faults and mitigates collateral damage to non-failing components when failures occur.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiments described below relate to a system for providing electrical power to a plurality of first circuit boards coupled with a first backplane, each of the plurality of first circuit boards characterized by an electrical power requirement. The system includes a plurality of power supply sets, each of the plurality of power supply sets being exclusively coupled with one of the plurality of first circuit boards to supply electrical power, each of the power supply sets comprising a second circuit board having a first power supply mounted thereon and a third circuit board having a second power supply mounted thereon, the second and third circuit boards separate from the plurality of first circuit boards. Wherein each of the plurality of power supply sets is operative to distribute the electrical requirement of an associated of the plurality of first circuit boards among each of the first and second power supplies, such that the first power supply is operative to supply a portion of the electrical power requirement not supplied by the second power supply.
The preferred embodiments further relate to a method for supplying electrical power to a plurality of first circuit boards coupled with a first backplane, each of the plurality of first circuit boards characterized by an electrical power requirement. In one embodiment, the method includes providing a plurality of power supply sets, each of the plurality of power supply sets being exclusively coupled with one of the plurality of first circuit boards to supply electrical power, each of the power supply sets comprising a second circuit board having a first power supply mounted thereon and a third circuit board having a second power supply mounted thereon, the second and third circuit boards separate from the plurality of first circuit boards, and distributing the electrical requirement of an associated of the plurality of first circuit boards among each of the first and second power supplies for each of the plurality of power supply sets, such that the first power supply is operative to supply a portion of the electrical power requirement not supplied by the second power supply.
Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.